Tap structure



Patented Jan. 5, 1943 UNITED STATES TAR' STRUCTURE George Hohwart,Orchard Lake, Mich., assignor to Suprex Gage Company, Pleasant Ridge,Mich., a corporation of Michigan Application June 10', 1942, Serial No.446,516

6 Claims.

This invention relates to taps of the type employed for forming threadsin cylindrical bores and the principal object is the provision of a newand improved tap, by the use of which certain advantages are capable ofbeing realized.

Objects of the invention include the provision of a tap capable of beingemployed for threading the bore in a piece of work and to provide arelief at the root of the threads formed thereby; the provision of a tapwhich is capable of forming a thread in the bore of a piece of work toconform to the cross-sectional configuration of the threads of athreaded piece to be threaded thereinto and at the same time to providea relief for the crests of the threads of such threaded piece; theprovision of a tap having formed thereon two axially distinct groups ofcutting teeth and one group of which is formed to cut a thread in thebore of a piece of work in substantially exact accordance with thecross-sectional configuration of at least a portion of the depth of thethreads of a threaded part which is intended to be screwed thereinto,and the other group of which comprises cutting teeth which do notconform to the cross-sectional conguration of the threads of a threadedpiece intended to be screwed into the work but instead are arranged tocut a relief at the root of the threads in the work for the crests ofthe threads of the threaded part to be received thereby; the provisionof a construction as above described in which at least a portion of thecutting faces of one of the groups of cutting teeth on the tap are soconstructed and arranged. as to cut a` thread in a piece of Work ofapproximately the full cross-sectional conguration of that portion ofthe teeth of av threaded part adapted to be received thereby, and theremaining group of teeth are so constructed and arranged as to removemetal from the piece of Work over a lesser width than the teeth of thefirst group but to a greater depth; and the provision of a tap of thetype described in which the teeth of both groups are of generallytriangular cross-sectional conformation but the angle between the sidesof the cutting edges of one group is greater than the angle between thesides of the cutting edges of the other group and the depth of the teethof the rst group is less than the depth of the teeth of the secondgroup.

The above being among the objects of the present invention, the sameconsists in certain novel details of construction and combinations ofthe partsto be hereinafter described with refer- TENT ortica claimed,having the above and other objects in View. l

In the accompanying drawing which illustrates the suitable embodimentsof the present invention and in which like numerals refer to like partsthroughout the several different views.

Fig. 1 is a perspective View of a conventional y type of Iadjustablethread ring gage, in the production of which the present invention. isparence to the accompanying drawing, and then 55 ticularly adaptable;

Fig. 2 is an enlargedyfragmentary, sectional view taken diametricallythrough a thread ring gage and illustrating the preferred form ofthreads and relief at the roots of the threads provided therein and themanner in which a threaded part to be gaged thereby is intended to fitthe same;

Fig. 3 is a partially broken, partially sectioned I side `elevationalview of my improved tap;

Fig. 4 is an end View of the top shown in Fig. 3, looking from the rightas viewed in Fig. 3;

Fig. 5 is an enlarged, fragmentary, sectional view, taken diametricallythrough the tap shown in Fig. 3 and included withinthe circle 5illustrated in Fig. 3;

Fig. 6 is a view similar to Fig. 5 but of that portion included withinthe circle 6 of Fig. 3;

Fig. 7 is a View similar to Fig. 5 but illustrating a piece of workassociated therewith and the IBG threads formed in thevwork thereby;and,

Fig. 8 is a view similar to Fig. 6 but illustrating in section afragment of a piece of work associated therewith in the manner whichoccurs by the employment of the tap shownin Fig. 3.

The present invention has been provided primarily for the purpose offorming the threads in thread ring gages and for that reason thefollowing desoription and explanation will be limited to its applicationto such thread ring gages, but thoseskilled in the art will recognizeits adaptability to any use where it is desired to provide a relief atthe roots of the threads in any threaded bore and its application is,therefore, not limited to the manufacture of thread ring gagesonly.

In accordance with conventional practices and in accordance with ScrewThread Standards for larly to the so-called 60 V-threads. The reliefwhich is required at the roots of the teeth of a Go thread ring gage isof only half the width of that desired at the root of the teeth for theNot go thread ring gage, but nevertheless such relief is desired, and isrequired in the larger sizes of thread ring gages for well understoodreasons.

In accordance with conventional methods such relief is produced by atool in a lathe after the threads have been cut in the gage blank, andwhile this method is satisfactory in the larger sizes of thread ringgages, the diiculty in applying such methods to small thread ring gagesand particularly to those adapted to gage parts.

of less than one inch in diameter has beenl so great that therequirements of such relief-in such smaller sizes has been waived .andthreads of full V-character at the roots have been accepted. Even in thelarger size of gages it is difficult to centralize therelief withrespect to the roots of the threads as will be appreciated by thoseskilled in the art. Nevertheless, the desirability of such relief at theroots of the teeth. of all thread ring gages is still desirable andwould still be required in the smaller sizes if capable of beingprovided without involving too great an expense. The present inventionprovides a means by which such relief may be providedat the root of thethreads in a thread ring gage in an accurately centralized andeconomical manner regardless of the diameter of the work which is to begaged thereby and is equally applicable to gages adapted to gage partsless than an inch in diameter as it is to larger gages.

' It has heretofore been proposed to provide such relief by forming atap, the cutting teeth of which, and particularly the finishing teeth ofwhich, areA complementary in cross-sectional configuration with thedesired cross-sectional configuration of the threads, including reliefvat the roots thereof, desired in the final gage, but those skilled inthe art will appreciate the difficulty of accurately forming suchcutting teeth with each side of a tooth including cutting edge portionsdisposed at an angle with respect to each other, and because of thisdifculty such taps have had a Very limited use.

The present invention provides a tap by means of which both the threadsand the relief between them may be formed in the bore of a gage, but inwhich the sides of the cutting. teeth are. in all cases perfectlystraight in cross-sectional configuration, thus enabling them to beformed in an accurate, ,simple and economical manner. This isaccomplished by providing a tap with two axially distinct groups ofcutting teeth. The cutting teeth of one of these groups may be andpreferably are identical to the teeth of a conventional tap except thatthe finishingv teeth thereof could be of fu'll triangular form, that is,without any crest, although thislatter feature is not essential in allcases.

The secondlgroup of teeth is also straight sided in cross-sectionalconfiguration and are disposed at the same helix cycle and incontinuation of the helix of the teeth of the rst group of threads soasto insure the relief cut thereby being centralized with the. roots ofthe threads cut by the firsty group, but the sides thereof inycross-sectional conguration are disposedat a lesser angle withv respectto each other than the sides of the teeth of the first group, andtheteeth of the second group are longer and project radially toa greaterdistance than the teeth of the first group. Consequently, these teeth ofthe second group, when following the teeth of the first group through abore, remove metal from the bore at the root of the threads formed bythe teeth ofthe first-mentioned group, thereby to provide the desiredrelief. The relative width and depth of such relief may, of course, becontrolled by the width and the length of the teeth of this second groupof teeth on the tap.

In constructing a tap in accordance with the present invention the teethof the rst group above described are preferably arranged toward theoperative end of the teeth from the teeth of the second group, althoughit will be recognized that this order may be reversed without affectingthe principles of the present invention. Where arranged as preferred, asabove described, when a tap is employed upon a piece of work, the firstgroup of teeth in operating upon the work will form threads in the borethereof substantially complementary in cross-sectional conguration tothe cross-sectional configuration of theY threads of the part to begaged thereby,v and after such threadshave been formed in the Work, thesecond group of teeth will then engage the. work and remove material atthe root of the threads thereof to form the desired relief.

Referring now .to the accompanying drawing, in Fig. 1 is illustrated aconventional form of American Standard adjustable thread ring gage.,v

This comprises a body portion I0 of disc-like conformation having acentral bore provided with threads I2 therein, providing Asurfaces forgaging the threads in a piece of work inaconventional manner. a pair. ofradial slots I4 extending outwardly froml its bore to render thebodyvflexible for adjusting purposes, and. a Vlockinggslot I6 whichextendsxfrom the bore through the peripheryand between oppositesides of.which .a suitableadjustable and locking mechanism. (not. shown) isemployed for adjusting the gage toY andlocking it'at the desireddiameter.

It is `assumed for. the purposes of` illustration only that the .threadgage illustrated in Fig.. 1 is a so called Not -go thread ring gage and.the tap shown in Fig.v 3 is constructed. `for the purpose of formingthethreads therein, but it will be understood. in this connection, andas will be .readily recognized by those skilled in the art, thatthe sameprinciples of constructionare equally applicable .to a tap which isadapted to form a Go thread ring gage.

Referring to Fig. 2 which illustrates the desired type ofengagementbetween the threads of the thread ringgageshown in Fig.. 1andthe pieceof work to. be gaged thereby, the gage being a Not go threadring gage, the crests of the threads I2 aretruncated as at I8.. for anamount equal to of the. pitch of the thread.

to `ensure that the. gage will check the. pitchY diameteronly of thepart beinggaged thereby.v

Forthe samereasons, a relief 20 -is formed at the root of .the threadsI2, and it. being considered that this -is a Not go. thread gage,.the.

Y plained. that where the gage is a Go thread ring gage the crests i8 ofthe threads I2 would be. of a width equal to one-fourth of they pitch ofthe threads. and the maxi-mum width ofthe relief 20. in such case wouldbe one-eighth the The body `II) is provided withv pitch of the threadsinstead of the figures Agiven and shown for a Not go gage.

In accordance'with the present invention, the threads I2 with the relief20 between them are formed by means of a tap, a preferred constructionfor which is illustrated in Figs. 3 and 4. This tap comprises a mainbody portion 30, having a squared driving end portion 32 in theparticular form shown, and having two groups A and B of cutting teethformed externally thereof at the opposite end. The teeth of groups A andB are, of course, formed in accordance with conventional practice, thatis, they are arranged helically around the axis of the body portion and,as illustrated in Fig. 4, are interrupted at intervals around theperiphery by longitudinally extending grooves 34 to presentcircumferentially directed cutting faces providing cutting edges. Thepitch of the teeth of both groups A and B is, of course, the same andthe teeth ofA group B are arranged as a continuation of the same helixthat the teeth of the group A are arranged in.

In Fig. 3, the groups A and B are shown as axially spaced from oneanother and while this is preferable from a manufacturing standpoint, itwill be recognized that it is not essential to the successful carryingout of the present The teeth of group A may be and are pref? erablyidentical to the teeth of a conventional tap of the same diameter andpitch, and in accordance with conventional practice those teeth at theentrance end of the tap are truncated for substantially their full depthand the amount of truncation decreases towards the opposite'end of theteeth until the last few rows of teeth present cutting faces fullycomplementary to the threads of the parts to be gaged thereby, with thepossible exception that these teeth are preferably brought to a sharppoint, and, accordingly, constitute finishing teeth. In other words,where the tap, as shown, is constructed to form 60 V- threads in a pieceof work, then the cross-sectional configuration of the finishing teethis of full V-like form and with opposite sides disposed at an angle of60 with respect to each other.

'Ihe teeth of group B are of greater length, that is, they projectradially outwardly from the axis of the main body portion to a greaterextent than the teeth of group A. Their opposite sides are disposed atan angle with respect to each other less than the corresponding angle ofthe sides of the teeth of group A. The reduction in angularity betweenthe sides of the teeth of group B as compared to those of the teeth ofgroup A is more or less unimportant as long as it is material, but wherethe teeth of group A are 60 teeth, the teeth of group A are preferablyformed withtheir opposite sides at an angle of approximately 30 withrespect to each other.

Thus, in employing the tap illustrated in Figs.

3 and 4 to form the threads l2 in a gage such as shown in Fig. l, thetap is threaded into the central bore of the main body I0 of the gageand when the finishing teeth 0f group A have engaged such bore, then thethreads therein will have assumed the cross-sectional configurationillustrated in Fig. 7, which is that configuration which has heretoforebeen acceptable for ring thread gages for gaging parts under one inch indiameter. However, in accordance with the present invention, the tapillustrated in Figs. 3

work l0 upon which the threads of group B thereof will engage the4 work.'I'hese teeth of group B being arranged-in the same vhelix as the teethof group A will, therefore, follow inV aligned relation to the teeth ofgroup A through the work I0 but, being narrower than the teeth A andhaving their opposite sides" disposed at a lesser angle than the teethof group A, they will only remove metal from the work l0 radiallyoutwardly beyond the points of intersection of their opposite sides withthe opposite sides of the threads l2 formed by the preceding teeth ofgroup A, in the manner illustrated in Fig. 8. In other Words, the teethof group B will have clearance between the sides of the threads l2 ofthe work formed by the teeth of group A except o-ver that width at'theroot of the threads i2 where the relief 20 is desired, and being longerthan the teeth of ygroup A will remove metal from the work to form suchclearance 20 central'- ly of the roots ofthe threads in all cases.

In view of the fact that the teeth of both groups A and B of the tapillustrated in Fig. 3 are formed with straight sides, each group may beformed iny accordance with the conventional practices followed informing conventional taps, and in forming the tap of the presentinvention the identical procedure followed in conventional practice ingrinding taps is followed in the present case in the grinding of thecutting teeth of each group A and B. Thus, the tap of the presentinvention may be constructed in an extremely accurate manner and at nota materially greater cost than in constructing a conventional tap ofequivalent size and of equivalent construction. However, by its use therelief which is required in ring thread gages may be accurately andeconomically obtained, regardless of the size of the gage. Therefore, itprovides a means which not only permits the desired relief to beobtained in ring thread gages in sizes heretofore substantiallyimpossible from a commercial standpoint, but permits the required relieftobe obtained in larger sizes in a more economical and efficient manner.

Having thus described my invention, what I claim by Letters Patent is:

l. A tap comprising a main body portion and two axially distinct groupsof cutting teeth thereon, the teeth of both groups being arranged in thesame helix about the axis of said main body portion, the cutting teethof both of said groups having straight sides and the angle between thesides of the cutting teeth of one of said groups being materially lessthan the angle between the sides of the cutting teeth of the other ofsaid groups, and said teeth of said one of said groups being longer thanthe teeth of the other of said groups and narrower at their bases thanthe teeth of said other group.

2. A tap comprising a main body portion and two axially distinct groupsof cutting teeth thereon, thev cutting teeth of one of said groups beingand 4 is continued to be threaded through the 75 arranged in a helixabout the axis of said main body portion and the cutting teeth of theother of said groups being arranged in a continuation of said helix, theteeth of one of said groups being narrower and longer than the teeth ofthe other of said groups. Y

3. A tap comprising a main body portion and two axially distinct groupsof cutting `teeth thereon, the cutting teeth of both of said groupshaving straight sides arranged in converging relation with respect toeach other and the teeth of one of said groups being narrower andprojecting raditwo axially distinct groups ofI cutting teeth thereon,the teeth of both of said groups being arrangedin a common helix aboutthe axis of said main body portion, that group of said teeth nearest theentering end of said tap having a uniform base width and a portion ofthem being truncated, the teeth of the second group having a` base Widthless than thebase width of the teeth of the first-mentioned group, andthe height of said teeth. of said second group being greater than theheight of said teeth of the rst group.

5. A tap comprising a main body portion and two axially distinct groupsof cutting teeth thereon, the cutting teeth of both of said groups beingarranged in alcommon helix about the axis of said main body portion, theteeth ofone ofY said groups all'having the same base Width and havingthe opposite sides thereof arranged at an angle of 60 degrees Withrespect to each other,

vthe teeth of the second offsaidgroups'.allhaving the same base Widthwhich isless than the 'base width of the rst-mentioned group and theteeth of said 'second group projecting radially from vthe .axis of'saidmain body portion t0 agreater distance than the teeth of the rstmentioned l group.

6. A'tap comprisinga main body portion and two axially distinct groupsof cutting teeth there- `on arranged in a common helix about the vaxisof lsaidmain'body portion, the teeth of one of said Igroups havingsidesv arranged at an angle-.0F60

degrees with respect to reach'otherrandpresent- -ing cutting edgesof auniform base Widthfthe -cutting teeth 'of the second of :saidgroupsvhaving the sides arranged at an angle of approximately 30 degreeswith respect to each other presenting cutting edges having avbase'vvidth less than the `base Width of the teeth ofthe rst-mentionedgroup and the teeth of said second'group projectingradially of said mainbody to a greater extent than the teeth of the rst-mentioned group.

GEORGE HOHWART.

